[ Organization | Stimulator Technology | Intra-cortical Electrodes 

Implant Package Design | Implant Electronic Design | Computer Interface ]

The first-generation intra-cortical visual prosthesis will use a 1024-channel implantable electrical stimulation system to drive micro-electrodes implanted into the visual cortex. The 1024-channel system will be comprised of four 256-channel implantable stimulator modules, inductively powered by a single extra-corporeal transmitter. Presently we are evaluating a hermetically-sealed, stimulator module (29.2mm (W) x 29.2mm (L) x 6 mm (H)) to establish basic feasibility of fabricating a fully implantable cortical stimulator. Although the requirements of the stimulator module are challenging, we feel that the state-of-the-art in BiCMOS circuit design, subminiature connectors, and ceramic hermetic packaging are sufficiently advanced to permit its fabrication.

Figure 4                                    Figure 5

Each 256-channel stimulator module is comprised of four individual 64-channel Submodules, shown in Figure 4, above. The rationale behind the use of 4 individual Submodules, each driving 64 of the 256 microelectrodes, per module, is two-fold. First, four, vertically-stacked, Submodules permit a more efficient use of the allowable volume than would be possible with a planar design. Second, since each Submodule is electrically and physically separate, the resulting redundancy enhances the overall system reliability. Within each Submodule, each electrode has a dedicated digitally-controlled 0-64 µA biphasic current driver and a 0-750 µsec pulse-width timer, contained within a DAC cell. Eight DAC cells are combined in one 8-channel Block Chip, shown in Figure 5, that uses a serial data input. Presently, our 8-channel Block Chip is a mature design, being used in various laboratories studying neural stimulation. All integrated circuits used in the Visual Prosthesis are designed at, and their layout is performed at IIT.

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